1. Field of the Invention
The present invention relates generally to field of facsimile machine communication and more particularly to increasing delay tolerances between two facsimile machines communicating via a wide area network.
2. Description of Background Art
Conventional facsimile stations, hereafter referred to as faxes, communicate with each other using a tonal or binary coded facsimile procedure and a modulation technique during each of several communication phases of a communication session. For example, the International Telecommunications Union (ITU) recommendation T.30 identifies five transmission phases. These phases are the: (1) call set-up phase; (2) pre-message identification and facilities selection phase; (3) message transmission phase; (4) post message procedures phase; and (5) call release phase. One feature of many transmission protocols, including the ITU T.30 transmission protocol, is that after one of a particular set of command signals is transmitted by a first fax, the first fax will "time-out" if a response signal, typically generated by a second fax at a remote location relative to the first fax, is not received by the first fax within a predefined time-out period. This time-out period varies for each transmission protocol and is frequently a time range. For example, in the ITU T.30 transmission protocol the time-out period can range from 2.55 seconds to 3.45 seconds, i.e., 3.0 seconds .+-.0.45 seconds (15%), after the transmission of the command signal depending upon the implementation of the protocol by a particular fax. A transmission protocol can handle time-out events in a variety of ways. This may include resending the command or disconnecting the session.
Reasons for not receiving a response signal within the time-out period include (1) network congestion; (2) network transmission delays, e.g., transmission delays introduced by satellites; (3) losing the response signal; (4) network jitters, and (5) network errors. Another time-out variable when using the T.30 protocol is that the T.30 protocol does not specify a fax machine turn-around time. If the reason for not receiving the response signal is other than having a lost response signal, it is generally ineffective for the fax to retransmit the command because its response will most likely exceed the time-out period. Instead, what is needed is a system and method that extends the period for response without altering the length of the time-out period defined in the transmission protocol.
One possible solution is to alter the time-out period defined by the transmission protocols. A problem with this solution is that the transmission protocols are frequently supported and interpreted by software within each fax. Therefore, in order to modify the transmission protocols, the software within these existing faxes must be modified. Such a solution would be expensive and difficult to implement.
During the pre-message identification and facilities selection phase, the faxes perform a handshaking operation that identifies, among other items, the type of fax, the transmission speed, and the modulation technique that is to be used during the communication session. One problem that is encountered when attempting to extend the delay tolerance of the faxes is that the protocol used by the faxes can be a proprietary protocol, or an infrequently used protocol. In the aggregate, these additional protocols are expensive to support because of the required memory space necessary to interpret and implement these prototypes. In addition, since many proprietary protocols are not published, extending the response signal delay tolerances of the communication session is difficult to accomplish when the faxes are utilizing such a proprietary protocol. Similarly, during the pre-message identification and facilities selection phase, the faxes agree on a signal modulation technique, e.g., the International Consultative Committee for Telephone and Telegraph (CCITT) recommendation V.29. It is difficult to support all modulation techniques because of the memory requirements and processing requirements demanded of the system. For example, each new fax model would need to be supported since each may have its own proprietary standard and, since many fax machines are designed for communications over a full duplex public switched telephone network (PSTN), these proprietary protocols may exceed the permitted bandwidth on the WAN. Therefore, what is needed is a system and method that ensures that two faxes communicate using one of a predefined, e.g., standard, set of supported transmission protocols and ensures that the faxes use one of a predefined set of modulation techniques.
Accordingly, what is needed is a system and method for: (1) extending the time period at which a response signal can be received before a time-out occurs even when the delay exceeds the time-out period defined in the transmission without altering the length of the time-out period defined in the transmission protocols; (2) ensuring that the two faxes communicate using one of a predefined set of transmission protocols; and (3) ensuring that the two faxes communicate using one of a predefined set of signal modulation techniques.